Sequential imaging apparatus

ABSTRACT

For use in medical imaging, an indexing assembly provides repeatable indexing movement of a joint in predetermined angular increments between sequential index positions. Means are provided for limiting movement of the joint to the next selected index position without skipping any index positions. The apparatus is contained entirely within, for example, a primary imaging coil of an MRI apparatus, and is patient directed.

RELATED APPLICATIONS

This application is a continuation-in-part of earlier filed co-pendingapplication Ser. No. 07/802,358, filed Dec. 4, 1991 by Peter M. Bonuttiand entitled Apparatus and Method for Use in Medical Imaging. Thebenefit of the earlier filing date of the aforementioned applicationSer. No. 07/802,358 for all subject matter common with this applicationis hereby claimed.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to medical imaging apparatus. Moreparticularly, the present invention relates to apparatus for use inimaging body parts such as joints, in applications such as magneticresonance imaging, CAT scanning, X-ray imaging, etc.

2. Description of the Prior Art

Human body parts such as joints can be imaged with magnetic resonanceimaging apparatus, CAT scanners, X-ray machines, and other types ofimaging apparatus. A typical medical imaging apparatus can image a jointsuch as a knee joint in almost any single orientation, limited only bythe physical dimensions of the imaging device. However, a typicalimaging apparatus is not capable of taking sequential images of a jointin predetermined selected orientations, in a repeatable manner. Thevarious bones, cartilage, ligaments, etc., assume different positionsand orientations when the joint is flexed or extended. Imaging a jointin only one orientation may not reveal defects or disease which isvisible only in certain orientations of the joint. Also, imaging a jointin only one orientation does not allow a doctor to study the full rangeof motion of the joint. Accordingly, it would be desirable to provideapparatus allowing for sequential, repeatable imaging of a joint inpredetermined selected orientations.

SUMMARY OF THE INVENTION

In one embodiment, the present invention is an indexing assembly forimaging a joint of a patient, the joint being movable into a pluralityof different orientations. The indexing assembly includes an indexmember connected with the joint for movement with the joint. The indexmember has a plurality of sequential index positions. A blocking memberis movable relative to the index member between a first positionblocking movement of the index member out of any one of the sequentialindex positions and a second position not blocking movement of the indexmember. The joint is imaged with the index member in one index positionand the blocking member in the first position. After the joint isimaged, the blocking member is moved to the second position to releasethe index member. The patient moves the index member to the nextsequential index position. The indexing assembly includes limiting meansfor limiting movement of the index member to movement into the next oneof the sequential index positions upon movement of the index member outof any one of the sequential index positions.

Almost all the parts of the indexing assembly, including the indexmember and the blocking member, are disposed inside the primary imagingcoil and closely adjacent to the joint during imaging of the joint. Theonly parts remote from the joint are a release control member forengagement by the patient and a connecting member connecting the releasecontrol member with the blocking member.

In another embodiment of the invention, an indexing assembly is providedfor indexing the knee joint through its range of motion about an axisparallel to the plane of the table. The patient lies on his back on theimaging table, with the knee raised up off the table. As the patientmoves his foot up and down, the knee joint is flexed and extendedthrough its range of motion. The indexing assembly is attached to theend of the imaging table. This allows the patient's foot to drop downbelow the top of the table, when the index assembly is moved to a lowposition. Thus, the knee joint can be moved through a greater range ofmotion than if the foot could not drop below the top of the table.Accordingly, the physician can image the knee joint through a greaterrange of motion. This provides substantial advantages as compared toprior art imaging in which the patient's entire body remains above thetop of the imaging table.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other features of the present invention will becomeapparent to one skilled in the art to which the present inventionrelates upon consideration of the following description of the inventionwith reference to the accompanying drawings, wherein:

FIG. 1 is a perspective view of a sequential imaging apparatus inaccordance with the present invention, showing a knee joint in positionto be imaged;

FIG. 2 is an exploded perspective view of the imaging apparatus of FIG.1;

FIG. 3 is a top plan view with parts removed of the imaging apparatus ofFIG. 1 in a locked condition;

FIG. 4 is a fragmentary sectional view with parts removed showingportions of the imaging apparatus in a locked condition;

FIG. 5 is a view similar to FIG. 4, showing the imaging apparatus in anunlocked condition;

FIG. 6 is a view similar to FIG. 3 showing the imaging apparatus in anunlocked condition;

FIG. 7 is a fragmentary sectional view with parts removed showing therelative positions of the plunger and cocking pin when the apparatus isin the locked condition;

FIG. 8 is a view similar to FIG. 7 showing the relative positions of theplunger and cocking pin when the apparatus is in the unlocked position;

FIG. 9 is a perspective view of an imaging apparatus and index assemblyin accordance with a second embodiment of the invention;

FIG. 10 is a side elevational view of the apparatus of FIG. 9 showingthe index assembly in first and second index positions;

FIG. 11 is a sectional view taken along line 11--11 of FIG. 10 withparts removed, showing the index assembly in a first index position;

FIG. 11A is a view similar to FIG. 11 showing the index assembly in asecond index position;

FIG. 12 is an enlarged fragmentary sectional view of a coil supportportion of the apparatus of FIG. 9; and

FIG. 13 is an enlarged fragmentary sectional view of a cuff and legplate portion of the apparatus of FIG. 9.

FIG. 14 is a perspective view of a magnetic resonance imaging apparatusin accordance with the present invention.

DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

The present invention relates to sequential imaging apparatus, andparticularly to apparatus for sequential imaging of a joint in animaging apparatus such as a magnetic resonance imaging apparatus. Thepresent invention is applicable to various imaging apparatusconstructions. As representative of the present invention, FIG. 1illustrates an index assembly 10 for indexing movement of a knee jointin a direction parallel to the plane of an imaging table and about anaxis normal to the plane of the imaging table.

FIG. 14 schematically illustrates a known patient support table 16 forsupporting a patient during imaging inside a known primary coil 14 of aknown magnetic resonance imaging unit 12. The table 16 is supported forsliding longitudinal movement into an out of the primary coil 14 in aknown manner. The index assembly 10 is positionable on the table forsliding longitudinal movement into and out of the primary coil 14.

The index assembly 10 includes a generally planar base 20 having anupper major side surface 22 (FIG. 2). An opening 24 extends downwardlyinto the base 20 from the upper major side surface 22 of the base.

Four risers 26 are fixed to the base 20 and project upwardly from theuppermajor side surface 22 of the base. The risers 26 support agenerally planarupper panel 30 at a location spaced from and parallel tothe base 20. Four screws 32 extend through openings 34 in the upperpanel 30 and into the risers 26, to secure the upper panel 30 to thebase 20. An opening 36 extends through the upper panel 30. The opening36 is coaxial with the opening 24 in the base 20.

A central support shaft 40 has its lower end received in the opening 24of the base 20 and its upper end extending through the opening 36 in theupper panel 30. The central support shaft 40 is rotatable relative tothe base 20 and to the upper panel 30 about an axis 42 (FIGS. 4 and 5).

A tray 50 (FIG. 2) is fixed, in any suitable manner, to the upper end ofthe central support shaft 40. The tray 50 is rotatable with the centralsupport shaft 40, relative to the base 22 and the upper panel 30. Thetray50 has a horizontal tray portion 52 and a vertical tray portion 54fixed toeach other. The horizontal tray portion 52 has an upper majorside surface 56. Two leg straps 58 and 60 are fixed to the tray 50.

An index disk 70 is fixed for rotation with the central support shaft40. The index disk 70 is cylindrical in shape and has a flat upper majorside surface 72 and a cylindrical outer side surface 74.

A plurality of trip pins 76 are disposed in a circular pattern on theindexdisk 70 about the axis 42. The trip pins 76 extend upwardly fromthe upper major side surface 72 of the index disk 70. The radialdistance from the axis 42 to each trip pin 76 is the same. All of thetrip pins 76 are of the same dimensions and configuration. Thus, as theindex disk 70 rotates about the axis 42, the trip pins 76 revolve in onecircular path about theaxis 42. The radially outermost surfaces of thetrip pins 76 describe a circular path 78 indicated in dashed lines inFIGS. 3 and 6.

The trip pins 76 are spaced about the axis 42 in equal angularincrements. In the illustrated embodiment, twenty-four trip pins 76 areprovided, withan angular spacing of 15° between each trip pin. However,a different number of trip pins 76 can be provided, with correspondinglydifferent spacing therebetween, as described below in greater detail.

A plurality of index openings 80 in the index disk 70 extend radiallyinwardly from the cylindrical outer side surface 74 of the index diskfor a relatively short distance toward the axis 42. There are as manyindex openings 80 as there are trip pins 76. The angular spacing betweenthe index openings 80 is the same as the angular spacing between thetrip pins76. Thus, in the illustrated embodiment, twenty-four indexopenings 80 are provided, each spaced 15° apart from the next, aroundthe outer circumference of the index disk 70. As can be seen in FIGS. 3and 6, the index openings 80 are staggered relative to the trip pins 76.The index openings 80 are spaced circumferentially equidistant betweenpairs of adjacent trip pins 76.

A support block 90 is fixed to the base 20 at a location spaced from theindex disk 70. An end portion 92 (FIG. 2) of the upper panel 30 projectsover the support block 90. A cylindrical plunger opening 94 (FIG. 4)extends through the support block 90 in a direction to intersect theaxis 42. The support block 90 has a reduced diameter neck portion 96 atthe outer end of the plunger opening 94.

A plunger 100 is slidably received in the plunger opening 94 in thesupportblock 90. The plunger 100 has a cylindrical outer surface 102(FIGS. 7 and 8). The plunger 100 has a head end portion 104 (FIG. 4) anda trailing endportion 106. An annular groove 108 in the plunger 100 isdisposed between the head end portion 104 and the trailing end portion106.

An elongate member 110 (FIG. 3) is connected to the trailing end portion106 of the plunger 100. The elongate member 110 (preferably a cord or astring) extends longitudinally through a compression spring 112 (FIGS. 3and 4) disposed between the trailing end portion 106 of the plunger 100(FIG. 4) and the support block neck portion 96. The spring 112 biasesthe plunger 100 relative to the support block 90 in a direction to theleft asviewed in FIGS. 3-6, toward the index disk 70.

A swivel pin 120 is fixed to and extends upwardly from the support block90. The swivel pin 120 (FIG. 4) is received in an opening 124 in atrigger122. The swivel pin 120 supports the trigger 122 for pivotalmovement aboutthe swivel pin relative to the base 20.

The trigger 122 has a head end portion 126 which extends over the indexdisk 70. The head end portion 126 of the trigger 122 extends over theindex disk 70 to a location radially inwardly of the path 78 defined bythe radially outermost surfaces of the trip pins 76. Thus, as the indexdisk 70 rotates, the head end portion 126 of the trigger 122 isengageableby the trip pins 76.

A trailing end portion 128 of the trigger 122 extends between opposedtrigger biasing assemblies 130 and 132. The trigger biasing assembly 132(FIGS. 3 and 6) includes a housing 134 (FIGS. 4 and 5) fixed to thesupport block 90. A biasing block 138 (FIG. 3) is received in acylindrical opening in the housing 134. A compression spring 136 biasesthe biasing block 138 against the trailing end portion 128 of thetrigger 122, in a direction toward the bottom of FIGS. 3 and 6.Similarly, the biasing assembly 130 includes a compression spring 142which urges a biasing block 144 in the opposite direction against thetrailing end portion 128 of the trigger 122, that is, toward the top ofFIGS. 3 and 6. The biasing effects placed on the trigger 122 by thebiasing assemblies 130 and 132, respectively, are equal, so that thetrigger 122 normally maintains the position illustrated in FIG. 6aligned with the axis 42 and with the plunger 100.

The trigger 122 includes a cocking pin 150. The cocking pin 150 extendsdownwardly from the trailing end portion 128 of the trigger. The cockingpin 150 extends downwardly far enough so that as the trigger 122 pivotsabout the swivel pin 120, the cocking pin 150 can engage the outer sidesurface 102 of the plunger 100, as seen in FIG. 7. The lower end 152 ofthe cocking pin 150 can enter the groove 108 in the plunger 100, as seenin FIG. 8.

The index assembly 10 is adapted for imaging of the knee joint of apatientlying on a table inside a primary imaging coil of a magneticresonance imaging apparatus. The patient supinates the foot and leg sothat the lower leg fits along the upper major side surface 56 of thehorizontal tray portion 52 of the tray 50, as illustrated in FIG. 1. Thestraps 58 and 60 are placed around the lower leg to stabilize the limband secure the lower leg to the tray 50.

The index assembly 10 is initially in a locked condition as illustratedin FIGS. 3 and 4. One index opening 160 of the index openings 80 isaligned with the plunger 100. The spring 112 biases the head end 104 ofthe plunger 100 into the index opening 160. The plunger 100 blocksrotation ofthe index disk 70 about the axis 42. Because the index disk70 cannot rotate, the central support shaft 42 and the tray 50 alsocannot rotate. Thus, the patient's lower limb, which is strapped to thetray 50, is stabilized and a clear image of the knee joint can be taken.

When the index assembly 10 is in the locked condition shown in FIGS. 3and 4, the trigger 122 is in a pivoted orientation not pointing towardthe axis 142 and not parallel to the plunger 100. The cocking pin 150 ofthe trigger 122 extends below the top of the plunger 100. The cockingpin 150 engages along the cylindrical outer side surface 102 of theplunger 100, as illustrated in FIG. 3 and in more detail in FIG. 7. Theplunger 100 holds the cocking pin 150 and the trigger 122 in thispivoted position illustrated in FIG. 3, against the biasing effect ofthe spring 136.

When it is desired to index the knee joint in a different orientation,the index assembly 10 must be released to allow the index disk 70 tomove to the next index position. The patient pulls a handle 164 attachedto the elongate member 110 extending from the plunger 100. The plunger100 is retracted against the bias of the spring 112, from the blockingposition illustrated in FIGS. 3 and 4 to the position illustrated inFIGS. 5 and 6.The head end portion 104 of the plunger 100 is retractedout of the index opening 160. The index disk 70 is then free to rotateif the patient movesthe joint.

When the plunger 100 is retracted by the patient, the groove 108 in theplunger moves into a position adjacent the cocking pin 150. The cockingpin 150 is then free to move laterally into the groove 108 in theplunger 100. The biasing effect of the spring 136 pivots the trigger 122so that the cocking pin 150 moves into the groove 108 of the plunger100, centeredover the plunger. The trigger 122 is in a cocked position.The springs 136 and 142 hold the trigger 122 centered between them, andthe index assembly10 is then in the position shown in FIGS. 5, 6, and 8.The engagement of the cocking pin 150 in the groove 108 of the plunger100 blocks movement of the plunger 100 in a direction toward the indexdisk 70. The patient can release the handle 164, and the plunger 100will not move into engagement with the index disk 70 or into any of theindex openings 80.

The patient can then move the knee joint toward the next sequentialindex position at which an image is to be taken. As the patient flexesor extends the knee joint, the limb portion strapped to the tray 50moves thetray 50 and causes the index disk to rotate, for example, inthe direction indicated by the arrow 166 in FIG. 3. As the index disk 70rotates, the trip pin closest to the trigger 122, which is the trip pindesignated 168 in FIG. 3, engages the head end portion 126 of thetrigger 122. The trip pin 168 pivots the trigger 122 about the swivelpin 120, from the cocked position illustrated in FIGS. 5 and 6 backtoward the uncocked position illustrated in FIGS. 3 and 4.

When the trigger 122 pivots, the cocking pin 150 moves out of the groove108 in the plunger 100, from the position illustrated in FIG. 8 to theposition illustrated in FIG. 7. When the cocking pin 150 moves out ofthe groove 108 in the plunger 100, the plunger is then free to movelongitudinally in the plunger opening 94 in the support block 90. Thebiasing effect of the plunger spring 112 causes the plunger 100 to movetoward the index disk 70. The head end portion 104 of the plunger 100engages the cylindrical outer side surface 74 of the index disk 70. Astheindex disk 70 continues to rotate in the direction indicated by thearrow 166, the next sequential index opening 162 moves into positionbetween theaxis 42 and the plunger 100, and the head end portion 104 ofthe plunger moves into the index opening 162, blocking further rotationof the index disk 70.

Rotation of the index disk 70 by the patient results in almost immediateengagement of the trigger 122 by the trip pins 76. This engagementreleases the plunger 100, again almost immediately, and the plunger 100isin position to engage the next succeeding index opening 80 along theouter circumferential surface 74 of the index disk 70. Thus, theconstruction ofthe index assembly 10 assures that whenever the patientreleases the index assembly 10 by pulling on the handle 164, and thenmoves his knee joint, the index assembly 10 will lock in a next indexposition a given number ofdegrees from the previous index position. Inthe illustrated embodiment, that number of degrees is 15°. That numberof degrees can be changed by placing the index openings 80 and the trippins 76 at differentangular spacings around the index disk 70. Forexample, if seventy-two trippins 76 are provided, spaced 5° apart, andan equal number of index openings 80, then the movement of the indexdisk will be automatically limited to 5° of indexing each time. Thus, nomatter how fast the patient flexes or extends his leg to rotate theindex disk 70, the plunger100 will always engage in the next sequentialindex opening 80 in the indexdisk 70. This assures that a preciserepeatable sequence of images can be taken using the index assembly 10.

In the illustrated embodiment, the index assembly 10 is used in amagnetic resonance imaging application. Therefore, all of the parts ofthe index assembly 10 are made of nonferromagnetic materials.Preferably, the majority of the parts of the index assembly 10 are madeof polyethylene orof Delrin® brand plastic. The plunger spring 112 andthe trigger biasing springs 136 and 142 can be made of beryllium copperor of a similar nonferromagnetic material having the desired springcharacteristics. The straps 58 and 60 for stabilizing the patient's legtothe tray 50 can be made of nylon with suitable fasteners such asVelcro® brand fasteners. The elongate member 110 can be a simple stringor cord made of fabric or plastic.

It should be understood that the present invention is not limited toimaging of a knee joint, and that the present invention is not limitedto imaging in a magnetic resonance imaging apparatus. The principles ofthe illustrated indexing assembly are applicable to imaging of almostany joint. Thus, the indexing assembly 10 can be configured to supportother joints such as an elbow joint, an ankle joint, a wrist joint, or ashoulder joint. Sequential imaging of all these joints can be useful. Anindexing assembly in accordance with the present invention can also beused in conjunction with a CAT scanner, an X-ray imaging apparatus, orother types of imaging apparatus.

It can thus be seen that the present invention provides an indexassembly 10 for imaging a joint of a patient movable into a plurality ofdifferent orientations. The index assembly 10 includes an index disk 70connected for movement with the joint by the tray 50. The index assembly10 has a plurality of sequential index positions, two of which areillustrated in FIGS. 3 and 6. A plunger 110 is movable relative to theindex disk 70 between a first position (illustrated in FIG. 3) blockingmovement of the index disk out of any one of the sequential indexpositions, and a second position (illustrated in FIG. 6) not blockingmovement of the index disk out of any one of the sequential indexpositions. An actuator 110, 164 is connected to the plunger 100 formoving the plunger between the first position and the second position.The index assembly includes trip pins 76and a trigger 122 for limitingmovement of the index disk 70 to movement into the next one of thesequential index positions upon movement of the index disk out of anyone of the sequential index positions.

It can further be seen that the present invention contemplates that theentire index assembly 10 is disposed inside a primary imaging coil of amagnetic resonance imaging apparatus or the like in a location closelyadjacent to a joint during imaging of the joint. The only parts remotefrom and not closely adjacent to the joint during imaging of the jointarea release control member or handle 164 and an elongate connectingmember 110 connecting the release control member with the plunger 100.These parts are also within the primary imaging coil as they are graspedby the patient's hand.

It can be further seen that the present invention provides an actuator164,110 operable by a patient and connected to the plunger 100 formoving the plunger 100 into a position to allow movement of the indexdisk 70 out of a sequential index position, subsequent to imaging of ajoint. The index assembly further includes a tray 50 and a centralsupport shaft 40 for transmitting the force of movement of the jointbetween different orientations to the index disk 70 to move the indexdisk into the next oneof its sequential index positions upon movement ofthe joint into a different orientation. Limiting means including thetrigger 122 is operable to move the plunger 100 back into its lockingposition in one of the index openings 80, to allow imaging of the jointin the next one of its different orientations.

In a second embodiment of the invention, an indexing assembly isprovided for movement of the knee joint about an axis parallel to theplane of an imaging table and in a direction transverse to the plane ofthe table. Thepatient lies on his back inside a primary imaging coil ofa magnetic resonance imaging apparatus, and moves his lower leg up anddown to extendand flex the knee joint. The knee is elevated so that theknee joint can bemoved through its full range of motion.

An index assembly 200 in accordance with the second embodiment of theinvention is illustrated in FIGS. 9-13. FIGS. 9 and 10 show portions ofanimaging table 202 which is slidable inside a primary coil (not shown)of a magnetic resonance imaging apparatus. The table 202 has an uppermajor side surface 203. The patient lies on a pad 204 on the table 202.The patient's head is towards the right as viewed in FIGS. 9 and 10. Thetable202, with the pad 204, is movable longitudinally in and out of theprimary coil. The table 202 is slid out to set up and place the patienton the table, then is slid in for imaging.

In addition to the primary coil, a known secondary coil assembly 206 maybeused to obtain a better image of the knee joint. The secondary coilassembly 206 includes a frame 208 with a lower frame portion 210 and twoupright frame portions 212 and 214. The secondary coil itself includes alower coil portion 216 fixed to the coil frame 208. An upper coilportion 218 is pivotally mounted at one end 220 to the frame 208. Theupper coil portion 218 is pivotable from the closed position shown inFIGS. 9 and 10 to an open position (not shown) to allow the patient'sleg to be placed inside the secondary coil from above. The upper coilportion 218 then is swung back to the closed position to image the kneejoint.

The coil lower frame portion 216 (FIG. 12) has on its lower surface arib 222 which extends parallel to the length of the table 202. The rib222 normally fits in a complementary groove 224 on the table 202, sothat the secondary coil assembly 206 is slidable along the table 202 toimage at various locations along the table. However, in accordance withthe presentinvention, the knee is raised up off the table 202 to allowimaging of the knee joint through its range of motion. Thus, thesecondary coil assembly 206 must also be raised up off the table 202.

A pair of coil support blocks 226 and 228 support the secondary coilassembly 206 in its raised position. Each coil support block has on itslower surface a rib 230 which fits into the groove 224 on the table 202.Each coil support block 226, 228 also has on its upper surface a groove232 which accepts the rib 222 of the coil lower frame portion 216. Thus,the coil support blocks 226 and 28 and the secondary coil assembly 206areslidable along the table 202 to image at various locations along thetable.Each coil support block 226, 228 has a fastener opening 234 forreceiving therethrough a suitable fastener (not shown) to secure thecoil support block to an existing opening 236 in the table 202. Eachcoil support block226, 228 also has an actuator passage 238 extendinglongitudinally through the coil support block in a direction parallel tothe length of the table 202, for a purpose to be described below.

A coil clip 240 attaches the secondary coil assembly 206 to the coilsupport block 226. A pair of thumb screws 242 fix the coil clip 240 tothecoil support block 226. A similar coil clip 246 holds the other endof the coil assembly 206 to the other coil support block 228.

A leg support wedge 250 raises the patient's knee so that it fits withinthe raised secondary coil assembly 206. The leg support wedge 250includesa lower wedge member 252, an upper wedge member 254, and twowedge uprights256 and 258. The lower wedge member 252 is disposed on thetable 202. The wedge uprights 256 and 258 support the upper wedge member254, at an angle, raised up from the lower wedge member 252. Thus, asthe patient lies on the pad 204 on the table 202, the leg support wedge250 raises thepatient's knee so that it fits within the secondary coilassembly 206.

The index assembly 200 includes a U-shaped index holder 260 (FIGS.9-11). The index holder 260 has a lower portion 262. A left support arm264 and aright support arm 266 extend upwardly from the index holderlower portion 262. Two fasteners 268 extend through the index holderlower portion 262 and secure the index holder 260 to an end surface 269of the table 202, asshown in FIGS. 9 and 10.

A pivot pin 270 (FIGS. 9 and 10) having an axis of rotation 272 extendsbetween the left and right support arms 264 and 266. The axis 272extends parallel to the plane of the table 202 and in a direction acrossthe widthof the table. The pivot pin 270 supports an index disk 280 forpivotal movement relative to the index holder 260. The index disk 280 isdisposed between the left and right support arms 264 and 266 of theindex holder. The index disk 280 is a part circular structure, shapedsomewhat like a piece of pie, having a flat upper end surface 282 and aflat lower end surface 284. An outer circumferential surface 286 extendsbetween the upper and lower end surfaces. A flat left outer side surface290 and a flat right outer side surface 292 are on opposite sides of theindex disk 280.

Two sets of index openings are arrayed on opposite sides of the indexdisk 280. The first or left set of index openings 294 extend inwardlyinto the index disk 280 from the left outer side surface 290 of theindex disk. Theindex openings 294 are arrayed in a part circular patternon the index disk280 with the axis 272 as the center of the pattern. Theindex openings 294 are all equally spaced from the axis 272. The indexopenings 294 are spaced from each other in equal angular incrementsabout the axis 272 and near the outer edge 286 of the index disk 280. Inthe illustrated embodiment, the index openings 294 are 20' apart fromeach other, althoughthis spacing could be different as described in moredetail below.

The second or right set of index openings 296 extend inwardly into theindex disk 280 from the right outer side surface of the index disk. Theindex openings 296 are arrayed in a part circular pattern on the indexdisk 280 with the axis 272 as the center of the pattern. The indexopenings 296 are all equally spaced from the axis 272. The indexopenings 296 are spaced from each other in equal angular incrementsabout the axis 272 and near the outer axis of the index disk 280. In theillustrated embodiment, the index openings 296 are 20° apart from eachother, although this spacing could be different as described in moredetail below.

The index openings 294 are staggered from the index openings 296. Thatis, the index openings 294 on one side of the disk 280 do not align withthe index openings 296 on the opposite side of the disk. Instead, theindex openings 294 are disposed so as to fall halfway between pairs ofindex openings 296 of the other set. Thus, there is a 10° angularincrement between an index opening 294 of one set and an adjacent indexopening 296 of the other set.

A leg plate 300 is fixed to the index disk 280 for movement with theindex disk. Three leg plate attachment screws 302 extend through the legplate 300 and through the upper end surface 282 of the index disk 280,to securethe leg plate to the index disk. The leg plate 300 is longenough to substantially support the lower leg of the patient.

Two slider grooves in the leg plate 300 extend the length of the legplate.A left slider groove 304 (FIGS. 11, 13) is shaped to receive atenon portion 306 of a cuff slider 308. A right slider groove 310extends parallel to the left slider groove 304, also for the length ofthe leg plate 300. The right slider groove 310 is similarly shaped toreceive the tenon portion 306 of the cuff slider 308. The cuff slider308 is slidable in one or the other of the slider grooves 304 and 306.

A leg cuff 312 is fixed to the slider 308 for movement with the slider.A plurality of cuff attachment screws 314 extend through the cuff 312into the slider 308 to secure the cuff to the slider. Thus, the cuff 312is slidable with the slider 308 on the index disk 280. As the index diskpivots about the axis 272, the cuff is free to slide along the upper endsurface 282 of the index disk. Two leg straps 315 (FIG. 9) are attachedtothe leg cuff 312. The straps 315 are wrapped around the lower leg ofthe patient to secure the lower leg to the cuff 312.

The index assembly 200 includes a left plunger assembly 312 and a rightplunger assembly 318, for controlling the pivotal location of the indexdisk 280.

The left plunger assembly 316 (FIG. 11) includes a left plunger supportblock 320 fixed to the index holder left support arm 264 by two screwfasteners 322. A left plunger 324 extends through a passage 326 in theleft plunger support block 320. The left plunger 324 has a trailing endportion 328 to which is connected a left plunger actuator 330. The leftplunger actuator 330 is a cord or string 332 having a handle or fingergrip 334 on its end remote from the left plunger 324. The actuator cord332 extends from the left plunger 324 through the actuator passage 238(FIG. 9) in the left coil support block 228, to a location where it canbegrasped by the patient's left hand.

The left plunger 324 projects from the left plunger support block 320into the index holder left support arm 264. A body portion 336 of theleft plunger 324 is received in a chamber 338 in the index holder leftsupport arm 264. A compression spring 340 is disposed in the chamber 338between the left plunger support arm 264 and the body portion 336 of theleft plunger 324. The compression spring 340 biases the left plunger 324towardthe index disk 280, in a direction to the right as viewed in FIG.9. A pulling force applied by the patient, through the actuator 330, issufficient to overcome the biasing effect of the spring 340 and retractthe left plunger 324 away from the index disk 280, in a direction to theleft as viewed in FIG. 9.

A leading end portion 342 of the left plunger 324 extends from the leftplunger body portion 336 toward the index disk 280. The leading endportion 342 is aligned with the track of the left index openings 294 inthe index disk 280. Thus, as the index disk 280 pivots about the axis272,the left index openings 294 sequentially come into position adjacentthe left plunger 324 so that the leading end portion 342 of the leftplunger can enter into a selected one of the left index openings toblock pivotal movement of the index disk. When the leading end portion342 of the left plunger 324 is not engaged in one of the left indexopenings 294 in the index disk 280, the leading end portion of the leftplunger rides along the left outer side surface 290 of the index disk,between the left index openings.

The right plunger assembly 318 (FIG. 11A) is similar to the left plungerassembly. The right plunger assembly 318 includes a right plungersupport block 350 fixed to the index holder right support arm 266 by twoscrew fasteners 352. A right plunger 354 extends through a passage 356in the right plunger support block 350. The right plunger 354 has atrailing end portion 358 to which is connected a right plunger actuator360. The right plunger actuator 360 is a cord or string 362 having ahandle or finger grip 364 on its end remote from the right plunger 354.The actuator cord 362 extends from the right plunger 354 through anactuator opening 335 (FIG. 9) in the right coil support block 228, to alocation where it can be grasped by the patient's right hand.

The right plunger 354 (FIG. 11A) projects from the right plunger supportblock 350 into the index holder right support arm 266. A body portion366 of the right plunger 354 is received in a chamber 368 in the indexholder right support arm 266. A compression spring 370 is disposed inthe chamber368 between the right plunger support arm 266 and the bodyportion 366 of the right plunger 354. The compression spring 370 biasesthe right plunger354 toward the index disk 280, in a direction to theleft as viewed in FIG.11A. A pulling force applied by the patient,through the actuator 360, is sufficient to overcome the biasing effectof the spring 370 and retract the right plunger 354 away from the indexdisk 280, in a direction to the right as viewed in FIG. 9.

A leading end portion 372 of the right plunger 354 extends from theright plunger body portion 366 toward the index disk 280. The leadingend portion 372 is aligned with the track of the right index openings296 in the index disk 280. Thus, as the index disk 280 pivots about theaxis 272,the right index openings 296 sequentially come into positionadjacent the right plunger 354 so that the leading end portion 372 ofthe right plunger354 can enter into a selected one of the right indexopenings to block pivotal movement of the index disk. When the leadingend portion 372 of the right plunger 354 is not engaged in one of theright index openings 296 in the index disk 280, the leading end portionof the right plunger rides along the right outer side surface 292 of theindex disk, between the openings.

The index assembly 200 in the illustrated embodiment is constructed forusein magnetic resonance imaging of a knee joint of a patient lying onhis back inside a primary imaging coil of a magnetic resonance imagingapparatus. The imaging table 202 is first slid out of the primary coilso the patient can lie down on the table. The secondary coil assembly206 is opened, by swinging the upper coil portion 218 away from thelower coil portion 216. The patient lies on the table 202 and rests hisupper leg on the leg support wedge 250. The lower leg rests on the cuff312. The patient's knee joint is disposed above the lower portion 216 ofthe secondary coil. The upper coil portion 218 is then repositioned overthe lower coil portion 216 for imaging of the knee joint. The straps 315are fitted around the lower leg to stabilize the joint and secure thelower leg to the cuff 312. The table 202 is then slid into the primaryimaging coil.

The index assembly 200 can be in any desired index position to start.For example, the index assembly 200 can be in the index position shownin solid lines in FIG. 10, in which the leg plate 300 and the cuff 312extendparallel to the plane of the table 202.

In this starting position, the various elements of the index assembly200 are in the positions shown in solid lines in FIG. 8 and in FIG. 9.The cuff 312 and the slider 308 are disposed at a relatively distallocation (to the left as viewed in FIG. 10) along the leg plate 300. Theleading end portion 342 of the left plunger 324 is engaged in a leftindex opening380 (FIG. 11) which is one of the plurality of left indexopenings 294 in the index disk 280. The right plunger 354 is not engagedin any of the plurality of right index openings 296 in the index disk280--instead, the leading end portion 372 of the right plunger is inabutting engagement with the right outer side surface 292 of the indexdisk. The engagement ofthe left plunger 324 in the index disk 280 blockspivotal movement of the index disk about the pivot pin 270. As a result,the cuff 312 and the lower leg are fixed in position, and a clear imageof the knee joint can be taken.

After the knee joint is imaged in this first index position, the patientgrasps the left actuator handle 334 and pulls on it. The force of thepatient's pulling is transmitted through the actuator cord 332 to theleftplunger 324. The left plunger 324 is retracted against the biasingeffect of the left plunger spring 340. The leading end portion 342 ofthe left plunger 324 comes out of the index opening 380 in the indexdisk 280.

At this point, the left plunger 324 no longer blocks pivotal movement ofthe index disk 280, and the index disk can move out of the first indexposition shown in solid lines in FIG. 11. Since the right plunger 354 isnot engaged in any of the plurality of right index openings 296 in theindex disk 280, the index disk is free to pivot about the axis 272. Theweight of the patient's lower leg, pressing down through the cuff 312,theslider 308, and the leg plate 300, causes the index disk 280 to pivotdownward in the direction indicated by the arrow 382 in FIG. 10. As theindex disk 280 pivots, the leading end portion 372 of the right plunger354 slides along the right outer side surface 292 of the index disk. Thebiasing effect of the right plunger spring 370 forces the leading endportion 372 of the right plunger 354 against the outer side surface 292ofthe index disk 280.

Once the index disk 280 has pivoted through an angle of 10°, the indexopening 384 (FIG. 11A), which is one of the plurality of rightindexopenings 296 in the index disk, becomes aligned with the rightplunger 354.The leading end portion 372 of the right plunger 354 movesinto the index opening 384. The engagement of the right plunger 354 inthe index disk 280blocks pivotal movement of the index disk 280 aboutthe axis 272. As a result, the cuff 312 and the lower leg are fixed in asecond index position, and a clear image of the knee joint can be takenin this second index position, in which the knee joint is moved 10° fromthe firstindex position.

Further images can be taken at succeeding 10° index positions, by havingthe patient actuate the right plunger 354, then the left plunger 324, insuccession. Thus, the physician can obtain a more complete pictureof thestructure and movement of the knee joint through its range of motion.

It can thus be seen that the index assembly 200 is constructed so that,upon patient release of one of the plunges 324 and 354 via its actuator,the index disk 280 will automatically move into the next sequentialindex position, without skipping any intervening index positions. Thisensures accurate and repeatable imaging sequences. If desired, ofcourse, the patient can actuate the index assembly 200 as many times asdirected between images, for example to take images at every 20° throughtherange of motion of the joint rather than every 10°. Imaging atotherangular increments can be provided by placing the index openings294 and 296 in the index disk 280 at different angular spacings, such as5°rather than 10°, etc.

As the knee joint is flexed (moved from a straighter position to a morebent position), the knee itself tends to rise, thus pulling the lowerleg closer toward the secondary coil assembly 206. The sliding movementof thecuff 312 on the index disk 280 accommodates this. As seen in FIG.10, the cuff 312 is in a more distal position along the index disk 280when the upper end surface 282 of the index disk is parallel to theplane of the table 202. When the knee joint is flexed and the index diskis moved to the second index position shown in phantom in FIG. 10, thecuff 312 and the slider 308 slide proximally (to the right as viewed inFIG. 10) along the index disk 280. Thus, the knee joint is not strainedbut instead is allowed to retain its normal configuration.

FIG. 10 illustrates movement of the index disk 280 through an angle of30° between the position shown in solid lines and the position shown inphantom. This is for purposes of clarity in the drawings. Showingtheindex disk 280 moved only through a 10° increment, for example, in FIG.10, would not show the pivotal movement so clearly. Thus, the 30° rangeof motion shown in FIG. 10 between the first index position shown insolid lines and the second index position shown in phantom would beachieved by indexing three times--left, right, and left.

As noted above, the index holder 260 is secured to the end surface 269of the table 202. This allows the patient's foot to drop down below theuppermajor side surface 203 of the table 202, when the index assembly200 is moved to a low position (past that shown in phantom in FIG. 10).Thus, theknee joint can be moved through a greater range of motion thanif the foot could not drop below the upper major side surface 203 of thetable 202. Accordingly, the physician can image the knee joint through agreater range of motion.

This mounting of the index assembly on the end of the table providessubstantial advantages as compared to prior art imaging in which thepatient's entire body remains above the top of the imaging table. Atypical imaging table is about 6" deep (tall). Thus, when a patient lieson the top of a table and inside the primary imaging coil, the tabletakesup 6" of vertical space inside the primary coil, space which canthen not be used for imaging. Mounting the index assembly on the end ofthe table in accordance with the present invention regains this 6" ofspace, and allows much greater range of imaging motion. The table worksfor the patient and physician, rather than against them. For example,the knee joint can be imaged through a range of about 60° with theindexing assembly 200, while the prior art images only allow imagingthrough a range of about 30°.

It should further be noted that the imaging apparatus in accordance withboth the first embodiment (FIGS. 1-8) and second embodiment (FIGS. 9-13)allow the patient to lie on his back inside the primary coil. Prior artimaging apparatus for indexing require the patient to lie on hisstomach. Since it takes two to five minutes for each image (cut), thepatient can be required to lie on his stomach inside a claustrophobicprimary coil for30 to 60 minutes to image a joint with prior art imagingapparatus. This isextremely uncomfortable. The patient's comfort isvastly increased by lyingon his back, and the imaging process isconsequently improved.

The known secondary coil assembly 206 is offset laterally from thelongitudinal center line of the table 202 so that the coil portions 216and 218 are not over the center line of the table 202 but rather areoffset slightly to one side. The secondary coil can be flipped 180°toplace the coil portions 216 and 218 offset slightly to the other sideofthe center of the table 202. Thus, clear images of the knee can betaken with the secondary coil with either the left or right knee jointin its normal position off the centerline of the body. To accommodatethis variance in imaging position, the leg plate 300 has both the leftslider groove 304 and the right slider groove 310. When the slider 308is placed in the left slider groove 304, the cuff 312 is in the properposition to image the left knee. When the slider 308 is placed in theright slider groove 310, the cuff 312 is then in the proper position toimage the rightknee.

As discussed above, the coil support blocks 226 and 228 (FIGS. 9-12) inthesecond embodiment of the invention raise the secondary coil assembly206 off its normal position on the table 202. It may be necessary ordesirableto set the secondary coil assembly 206 at different heightsrelative to thetable 202. If so, coil support blocks can be providedwith different heights to enable setting of the secondary coil assembly206 at different heights. Also, the leg support wedge 250 can bereplaced with similar wedges having different angles and heights, toraise the knee to differentheights above the table 202.

From the above description of the invention, those skilled in the artwill perceive improvements, changes and modifications in the invention.Such improvements, changes and modifications within the skill of the artare intended to be covered by the appended claims.

I claim:
 1. A method of imaging a knee joint of patient with an imagingunit, said method comprising the steps of gripping a lower portion of apatient's leg at a location below the knee joint with a cuff which isconnected with a rotatable member, positioning the knee joint in theimaging unit, bending the knee joint while the knee joint is in theimaging unit, moving the lower portion of the patient's leg along anarcuate path while bending the knee joint, rotating the cuff and themember under the influence of force applied against the cuff by thelower portion of the patient's leg and transmitted from the cuff to themember during bending of the knee joint, retaining the lower portion ofthe patient's leg against movement in a direction transverse to thearcuate path during bending of the knee joint, said step of retainingthe lower portion of the patient's leg against movement in a directiontransverse to the arcuate path including restraining the lower portionof the patient's leg against movement in a direction transverse to thearcuate path under the influence of force transmitted from the memberthrough the cuff to the lower portion of the patient's leg, and imagingthe knee joint when the lower portion of the patient's leg is at each ofa plurality of positions along the arcuate path.
 2. A method as setforth in claim 1 further including the steps of interrupting bending ofthe knee joint with the lower portion of the patient's leg at each ofthe plurality of positions along the arcuate path, and maintaining thelower portion of the patient's leg stationary in each of the pluralityof positions in turn while imaging the knee joint.
 3. A method as setforth in claim 2 wherein said step of positioning the knee joint in theimaging unit includes positioning the knee joint in the imaging unitwith an axis about which the member is rotatable extending through thepatient's leg.
 4. A method as set forth in claim 1 wherein said step ofrotating the cuff and the member includes rotating the cuff and memberabout an upright axis which extends through the patient's leg, said stepof moving the lower portion of the patient's leg along an arcuate pathincludes moving the lower portion of the patient's leg along a generallyhorizontal arcuate path.
 5. A method as set forth in claim 1 furtherincluding the step of moving the cuff relative to the member to changethe distance between the cuff and the axis of rotation of the memberduring performance of said step of moving the lower portion of thepatient's leg along an arcuate path while bending the knee joint.
 6. Amethod of imaging a knee joint of a patient while the patient is lyingon his or her back, said method comprising the steps of gripping a lowerportion of a patient's leg at a location below the knee joint with acuff which is connected with a rotatable member, positioning the kneejoint in the imaging unit with the patient lying on his or her back,bending the knee joint while the knee joint is in the imaging unit andwhile the patient is lying on his or her back, moving the lower portionof the patient's leg along an arcuate path while bendig the knee jointwith the patient lying on his or her back, rotating the cuff and themember about an axis extending through the member during bending of theknee joint while the patient is lying on his or her back, retaining thelower portion of the patient's leg against movement in a directiontransverse to the arcuate path during bending of the knee joint whilethe patient is lying on his or her back, said step of retaining thelower portion of the patient's leg against movement in a directiontransverse to the arcuate path including restraining the lower portionof the patient's leg against movement in a direction transverse to thearcuate path under the influence of force transmitted from the memberthrough the cuff to the lower portion of the patient's leg, and imagingthe knee joint when the lower portion of the patient's leg is at each ofa plurality of positions along the arcuate path while the patient islying on his or her back.
 7. A method as set forth in claim 6 furtherincluding the step of moving the cuff along a linear path extendingperpendicular to the axis about which the cuff and member are rotatableduring bending of the knee joint with the patient lying on his or herback.
 8. A method as set forth in claim 7 wherein said step of movingthe cuff along a linear path includes moving the cuff along the linearpath under the influence of force applied against the cuff by the lowerportion of the patient's leg during performance of said step of bendingthe knee joint while the knee joint is in the imaging unit and while thepatient is lying on his or her back.
 9. A method as set forth in claim 8wherein said step of rotating the cuff and the member about an axisextending through the member during bending on the knee joint while thepatient is lying on his or her back includes rotating the cuff and themember under the influence of force transmitted from the cuff to themember from the lower portion of the patient's leg.
 10. A method as setforth in claim 6 further including the steps of interrupting bending ofthe knee joint with the lower portion of the patient's leg at each of aplurality of positions along the arcuate path and while the patient islying on his or her back, and maintaining the lower portion of thepatient's leg stationary in each of the plurality of positions in turnwhile imaging the knee joint with the patient lying on his or her back.11. A method of imaging a knee joint of patient with an imaging unit,said method comprising the steps of gripping a lower portion of apatient's leg at a location below the knee joint with a cuff which isconnected with a rotatable member, positioning the knee joint in theimaging unit, bending the knee joint while the knee joint is in theimaging unit, rotating the cuff and the member about an axis duringbending of the knee joint, moving the cuff along a linear path relativeto the rotatable member under the influence of force applied against thecuff by the lower portion of the patient's leg while bending the kneejoint, and imaging the knee joint when the lower portion of thepatient's leg is at each of a plurality of positions in the imagingunit.
 12. A method as set forth in claim 11 wherein said step of movingthe cuff along a linear path includes moving the cuff toward the axisabout which the cuff and rotatable member rotate during bending of theknee joint to flex the patient's leg and moving the cuff away from theaxis about which the cuff and rotatable member rotate during bending ofthe knee joint to extend the patient's leg.
 13. A method as set forth inclaim 11 further including moving the lower portion of the patient's legalong an arcuate path while bending the knee joint, and retaining thelower portion of the patient's leg against movement in a directiontransverse to the arcuate path during bending of the knee joint, saidstep of retaining the lower portion of the patient's leg againstmovement in a direction transverse to the arcuate path includingrestraining the lower portion of the patient's leg against movement in adirection transverse to the arcuate path under the influence of forcetransmitted from the member through the cuff to the lower portion of thepatient's leg.
 14. A method as set forth in claim 11 wherein said stepof rotating the cuff and member about an axis including moving the cuffand member under the influence of force applied against the cuff by thelower portion of the patient's leg.
 15. A method as set forth in claim11 wherein said step of positioning the knee joint in the imaging unitis performed with the patient lying on his or her back, said steps ofbending the knee joint being performed with the patient lying on his orher back, and said step of imaging the knee joint being performed withthe patient lying on his or her back.
 16. A method as set forth in claim11 further including the steps of interrupting bending of the knee jointwhen the lower portion of the patient's leg is at each of the pluralityof positions in the imaging unit, and maintaining the lower portion ofthe patient's leg stationary in each of the plurality of positions inturn while imaging the knee joint.
 17. Apparatus for magnetic resonanceimaging a knee joint of a patient, said apparatus comprising a magneticresonance imaging unit, and positioning means for controlling bending ofthe patient's knee joint with the knee joint in said magnetic resonanceimaging unit, said positioning means including a base, a memberrotatable relative to said base about an upright axis with said memberat least partially in said magnetic resonance imaging unit, cuff meansfor holding a lower portion of the patient's leg at a location below theknee joint with the knee joint in said magnetic resonance imaging unitand with the patient's leg extending across said member through theupright axis about which said member is rotatable, and connector meansfor connecting said cuff means with said rotatable member and forrotating said rotatable member under the influence of force transmittedfrom said cuff means through said connector means to said rotatablemember from the lower portion of the patient's leg.
 18. An apparatus asset forth in claim 17 wherein said member has a circular configurationand the upright axis about which said member is rotatable extendsthrough the center of said member.
 19. An apparatus as set forth inclaim 18 wherein said positioning means includes a plurality of indexlocations disposed along a peripheral edge portion of said member, andmeans for engaging at least one of said index locations to hold saidmember against rotation about the upright axis during imaging of theknee joint in said magnetic resonance imaging unit.
 20. An apparatus asset forth in claim 17 wherein said positioning means includes surfacemeans disposed in a place extending perpendicular to the upright axisand connected with said member for at least partially supporting thepatient's leg during rotation of said member about the upright axis. 21.An apparatus as set forth in claim 17 wherein said connector means andcuff means cooperate to guide movement of the lower portion of thepatient's leg along an arc having a center of curvature located on theupright axis about which said member rotates.
 22. An apparatus as setforth in claim 17 wherein said positioning means includes an indexmechanism for retaining said member and the lower portion of thepatient's leg in each index position of a series of index positions inturn, said index mechanism including a plurality of index locationsdisposed in an arcuate array on said member, retainer means for engagingsad index locations, said retainer means being movable between anextended position engaging an index location and a retracted positionspaced from said index locations, biasing means for urging said retainermeans toward the extended position, latch means for retaining saidretainer means in the retracted position against the influence of saidbiasing means, said latch means being operable between a latch positionin which said latch means is effective to retain said retainer means inthe retracted position and a release position in which said latch meansis ineffective to retain said retainer means in the retracted position,and means for operating said latch means from the latch position to therelease position in response to rotational movement of said member aboutthe upright axis.
 23. An apparatus for magnetic resonance imaging a kneejoint of a patient, said apparatus comprising a magnetic resonanceimaging unit, and positioning means for controlling bending of thepatient's knee joint with the knee joint in said magnetic resonanceimaging unit, said positioning means including a base, a memberrotatable relative to said base with said member at least partially insaid magnetic resonance imaging unit, cuff means for holding a lowerportion of a patient's leg at a location below the knee joint with theknee joint in said magnetic resonance imaging unit, and connector meansfor connecting said cuff means with said member, said connector meansincluding means for enabling said cuff means to move relative to saidmember along a linear path in one direction during rotation of saidmember and flexion of the knee joint and for enabling said cuff means tomove relative to said member along the linear path in a directionopposite to the one direction during rotation of said member andextension of the knee joint, said cuff means being movable relative tosaid member along the linear path under the influence of forcetransmitted to said cuff means from the lower portion of the patient'sleg.
 24. An apparatus as set forth in claim 22 wherein said connectormeans includes surface means for forming a linear track connected withsaid member and a slider movable along the linear track and connectedwith said cuff means.
 25. An apparatus as set forth in claim 25 whereinsaid connector means transmits force from said cuff means to rotate saidmember under the influence of force applied against said cuff means bythe lower portion of the patient's leg.
 26. An apparatus as set forth inclaim 25 wherein said positioning means includes means for supportingsaid member for rotation about a horizontal axis.
 27. An apparatus asset forth in claim 25 wherein said positioning means includes aplurality of index locations disposed along a peripheral edge portion ofsaid member, and means for engaging at least one of said index locationsto hold said member against rotation during imaging of the knee joint insaid magnetic resonance imaging unit.
 28. An apparatus for magneticresonance imaging a knee joint of a patient, said apparatus comprising amagnetic resonance imaging unit, and positioning means for controllingbending of the patient's knee joint in said magnetic resonance imagingunit, said positioning means including a base, a member rotatablerelative to said base with said member at least partially in saidmagnetic resonance imaging unit, cuff means for holding a lower portionof a patient's leg at a location below the knee joint with the kneejoint in said magnetic resonance imaging unit, connector means forconnecting said cuff means with said member, an arcuate array of indexlocations connected with said rotatable member, said arcuate array ofindex locations having a center of curvature disposed on an axis aboutwhich said member is rotatable, an index element movable between anengaged position engaging at least one of said index locations to retainsaid member against rotation and a disengaged position spaced from saidindex location to release said member for rotation, biasing means forurging said index element toward the engaged position, and actuatormeans for moving said index element from the engaged position to thedisengaged position against the influence of said biasing means andunder the influence of force applied to said actuator means by thepatient.
 29. An apparatus as set forth in claim 28 further includingconnector means for enabling said cuff means to move relative to saidmember along a linear path in one direction during rotation of saidmember and flexion of the knee joint and for enabling said cuff means tomove relative to said member along the linear path in a directionopposite to the one direction during rotation of said member andextension of the knee joint, said cuff means being movable relative tosaid member along the linear path under the influence of forcetransmitted to said cuff means from the lower portion of the patient'sleg.
 30. An apparatus as set forth in claim 28 wherein said connectormeans includes means for rotating said rotatable member under theinfluence of force transmitted from said cuff means through saidconnector means to said rotatable member from the lower portion of thepatient's leg.
 31. An apparatus as set forth in claim 30 furtherincluding means for supporting said member for rotation about an uprightaxis which extends through the patient's leg.
 32. An apparatus as setforth in claim 30 further including means for supporting said member forrotation about a horizontal axis.